1. Field of the Invention
The present invention relates to ATM (asynchronous transfer mode) network technology, and in particular, to a dual SVC (switched virtual connection) system for an ATM device.
This application is based on Japanese Patent Application No. Hei 10-330369, the contents of which are incorporated herein by reference.
2. Description of the Related Art
In an ATM device, VPI (virtual path identifier) logically allows establishment of 256 ATM connections per line, and VCI (virtual channel identifier) logically allows establishment of 65536 ATM connections per VPI. The maximum number of SVCs (switched virtual connections) depends on the call processing performance and the storage capacity for the internal resources of the ATM device, and has increased recently as the performance of ATM devices has improved.
While ATM devices, such as ATM switching devices and ATM concentrators, handle a number of connections per line, and provide ATM communication service using a number of lines, various dual SVC systems are implemented in the ATM devices. The conventional dual SVC systems have the problems described below.
FIG. 8 is a diagram showing an ATM device using a conventional dual SVC system, and FIG. 9 is a diagram showing the sequence operation of the conventional dual SVC system for handling the SVC protocol.
Referring to FIGS. 8 and 9, the ATM device 200 which includes the conventional dual SVC system is connected to ATM members 10 and 11 through the SVC connection.
The ATM member 10 is connected to the ATM device 200 through a line 12, and the ATM member 11 is connected to the ATM device 200 through a line 13.
The ATM device 200 comprises: line terminating devices 7 and 8; active and standby switches 201a and 201b; and an information exchange device 206 between the active system and the standby system. The active and standby switches 201a and 201b comprise: signaling terminating functions 202a, 202b, 204a, and 204b; call process control functions 203a and 203b; and internal information management functions 205a and 205b. 
The call process control functions 203a and 203b hold routing setting information in the switches 201a and 201b. 
The ATM device 200 using the dual SVC system operates as follows.
SVC signaling information from the line 12 is sent by the line terminating device 6 to the active signaling terminating function 202a, and is processed by the active signaling terminating function 202a and the active call process function 203a. 
In this process, the signaling terminating function 202a and the call processcontrol function 203a continuously communicate with the active internal information management function 205a, obtain the internal resource information (B in FIG. 9) to execute the protocol procedure, and refer to the protocol information (A and Axe2x80x2 in FIG. 9).
Further, the call process control function 203a performs routing in the active switch 201a based on the result of the above process, and sends this routing information to the active internal information management function 205a as the ATM connection information B.
The active internal information management function 205a periodically transmits the internal resource information which is updated when processing the SVC protocol, the SVC connection information (B in FIG. 9), and the SVC protocol information (A and Axe2x80x2 in FIG. 9) to the standby internal information management function 205b through the information exchange device 206 as information for executing routing setting procedure.
This information is received by the standby internal information management function 205b. 
The standby signaling terminating function 202b and the call process control function 203b communicate with the standby internal information management function 205b in a manner similar to the active system, to execute the protocol process.
Based on the result of the process, the standby call process control function 203b performs routing in the standby switch 201b. Thus, the same SVC connection is established in both active and standby systems.
FIG. 10 is a diagram showing the second example of the ATM device using the conventional dual SVC system.
Referring to FIG. 10, ATM members 10 and 11 are connected via an ATM device 300 through the SVC connection. The ATM member 10 is connected to the ATM device 300 through a line 12, and the ATM member 11 is connected to the ATM device 300 through a line 13.
The ATM device 300 comprises: line terminating devices 7 and 8; and active and standby switch 301a and 301b. The active and standby switches 301a and 301b comprise: signaling terminating functions 302a, 302b, 304a, and 304b; and call process control functions 303a and 303b. 
The call process control functions 303a and 303b hold routing setting information in the switches 301a and 301b. 
The ATM device 300 using the conventional dual SVC system operates as follows.
SVC signaling information from the line 12 is sent to both active and standby switches 301a and 301b by the line terminating device 7. The signaling information is simultaneously processed by active and standby signaling terminating functions 302a and 302b and by the call process control functions 303a and 303b. 
As the result, the active and standby call process control functions 303a and 303b simultaneously perform routing in the active and standby switches 301a and 301b. 
Thus, the active and standby systems have the same SVC connection information.
However, the first example of the conventional dual SVC system, explained with reference to FIG. 8, has the following problems.
The first problem is that, as the number of SVC connections increases, the normal process performance including the call process by the active system is degraded.
The reason for this is that the amount of transferred data is increased because the information periodically exchanged between the active system and the standby system contains the internal resource information, which includes all the SVC connection information of the established and running connections, and the SVC protocol information.
The second reason is that, when the information transfer rate between the active and standby systems is increased, the possibility of inconsistencies in the internal information between the active and standby systems is increased.
The reason for this is that the time lag, between the establishment of the connection in the standby system based on the internal information from the active system and the occurrence of a problem in the active system, is increased, and that the information of the established or released SVC connection may be lost due to the time lag.
The second example of the conventional dual SVC system, explained with reference to FIG. 10, has the following problems.
The first problem is that, while, when an accident occurs in one of the two systems, the parts where the accident occurred are exchanged and the recovered system is registered as the standby system, the synchronization in setting between the active systems and the recovered standby system cannot be achieved.
The reason for this is that the information of the ATM connection, which is established or terminated in the time period from the occurrence of the accident to the registration of the recovered standby system, cannot be exchanged between the active and standby systems because the information exchange device is not prepared.
FIG. 11 is a diagram showing the third example of the ATM device 400 using the conventional dual SVC system (disclosed in Japanese Patent Application, First Publication No. Hei 10-084354).
Referring to FIG. 11, ATM members 10 and 11 are connected via an ATM device 400 through the SVC connection. The ATM member 10 is connected to the ATM device 400 through a line 12, and the ATM member 11 is connected to the ATM device 400 through a line 13.
The ATM device 400, which includes an active system and a standby system, comprises: line terminating devices 405a, 405b, 406a, and 406b; switches 401a and 401b; processors 402a and 402b; and an information exchange device 407 between the active system and the standby system. The processors 402a and 402b comprise: call process control functions 403a and 403b; and virtual neighbors switching functions 404a and 404b. 
All the SVC protocol process is executed by the processors 402a and 402b, and the SVC connection information is stored in the processors.
The processors 402a and 402b perform routing in the switches 401a and 401b based on the SVC connection.
In Japanese Patent Application, First Publication No. Hei 10-084354, the ATM device 400 using the conventional dual SVC system operates as follows.
The SVC signaling information from the line 12 is sent via the active line terminating device 405a to the active processor 402a, and is processed by the active call process control function 403a. 
As the result, the active call process control function 403a performs routing in the active switch 401a, produces information which is required for the routing in the standby switch 401b, in a data structure using a short data length, and sends it to the standby system through the information exchange device 406.
This information is received by the virtual neighbor switching function 404b, is reproduced as SVC signaling information, and is sent to the standby call process control function 403b. 
The standby call process control function 403b processes the reproduced signaling information in a manner similar to the active system, and performs routing in the standby switch 401b. Thus, the active and standby systems have the same SVC connection information.
Even when the number of connections is significantly increased in the third example of the conventional dual SVC system, the process time for the data transfer is not increased because the amount of data transfer between the active and standby systems is not increased, and the degradation of the process performance for the SVC protocol can be avoided.
Further, the interval between the data transfers between the active and standby systems is lengthened, and the possibility of inconsistencies in the SVC connection information between the active and standby systems is reduced.
The third example solves the difficulty in the synchronization of setting between the active and standby systems which arises in the second example shown in FIG. 10.
However, the third example of the conventional dual SVC system shown in FIG. 11 has the problems described below.
The first problem is that, as the number of calls increases, the performance in the call process is degraded.
The reason for this is that the structured data with the short data length, which includes only the information required for the routing, must be produced based on all the input SVC signaling information in a real-time manner by means of the call process module in the active and standby systems.
The second problem is that a special processor must be prepared to solve the first problem.
That is, the special processor produces the structured data with the short data length, which can be re-processed by the call process modules in the active and standby system and includes only the information required for the routing, in a real-time manner, preventing the degradation of the call process performance.
It is therefore an object of the present invention to provide an ATM device using an improved dual SVC system which can maintain the transmission of the ATM main signal information between ATM members through the SVC without any interruption even when switching between an active system and a standby system is performed, and in which the active system and the standby system have the same routing setting information and SVC connection information in a real-time manner.
In order to accomplish the above object, the dual SVC system for an ATM device, an ATM switching device, or an ATM concentrator, has an active switch system and a standby switch system, for connecting ATM members through the SVC (switched virtual connection) and routing ATM information. A device for sending SVC information from the active switch system to the standby switch system in a real-time manner is provided. When switching from the active system to the standby system occurs, the transfer of the ATM information through the SVC is maintained without any interruption. The SVC connection information is sent from the active switch to the standby switch at the time of establishment or termination of a call in the active switch system.
The active and standby switch systems comprise: switches for routing ATM information which includes signaling information; first and second signaling terminating devices connected to the first and second line terminating devices; call process control devices; and storage devices. An information exchange device is provided between the active switch system and the standby switch system.
The call process control device of the active switch system associates the signaling terminating devices according to information which is contained in an SVC protocol message processed by the signaling terminating device and to call setting signal information which is defined within the system and is stored in the storage device.
The call process control device of the active switch system stores the association information in the storage device as established or released SVC connection information, performs routing in the active switch system, and sends the SVC connection information to the call process control device of the standby switch system through the information exchange device.
The call process control device of the standby switch device performs routing in the standby system, based on the SVC connection information which is sent from the call process control device of the active switch device through the information exchange device, and stores the SVC connection information in the storage device of the standby switch system.
The first advantage is that, even when, in the ATM switching device or other ATM device with the dual switches, switching between the active and standby systems arises for some reasons, i.e., due to an accident in the switch, the transmission of the ATM main signal information through the SVC between the ATM members can be maintained without any interruption. This improves the reliability of the ATM network service using the ATM switching device or the ATM concentrator.
As the second advantage, even when the number of calls or the number of SVC connections increases, the data transfer is carried out between the active and standby systems, preventing the degradation of the call process performance because the information exchanged between the active and standby systems is not all the internal resource information which includes the SVC protocol information and the SVC connection information, but only the SVC connection information, and an additional process is not required. Further, the data exchange between the active and standby systems is performed, not at the time of change in status of the SVC, but at the time of the establishment or release of the SVC.